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Title: Signatures of moiré-trapped valley excitons in MoSe 2/WSe 2 heterobilayers

Abstract

The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect 1,2,3, tunable Mott insulators 4,5 and unconventional superconductivity 6. Moreover, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors 7,8,9, but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in a moiré potential in molybdenum diselenide (MoSe 2)/tungsten diselenide (WSe 2) heterobilayers. At low temperatures, we observe photoluminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 microelectronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, –15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley-pairing configurations. At twistmore » angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at a twist angle of approximately 60 degrees. This is consistent with the umklapp recombination of interlayer excitons near the commensurate 21.8-degree twist angle 7. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. Here, we report on opportunities to control two-dimensional moiré optics through variation of the twist angle.« less

Authors:
 [1];  [1];  [2];  [1];  [1];  [3]; ORCiD logo [3];  [2];  [1]
  1. Univ. of Washington, Seattle, WA (United States)
  2. Univ. of Hong Kong (China)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Programmable Quantum Materials (Pro-QM); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1513372
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Volume: 567; Journal Issue: 7746; Journal ID: ISSN 0028-0836
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Seyler, Kyle L., Rivera, Pasqual, Yu, Hongyi, Wilson, Nathan P., Ray, Essance L., Mandrus, David G., Yan, Jiaqiang, Yao, Wang, and Xu, Xiaodong. Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers. United States: N. p., 2019. Web. doi:10.1038/s41586-019-0957-1.
Seyler, Kyle L., Rivera, Pasqual, Yu, Hongyi, Wilson, Nathan P., Ray, Essance L., Mandrus, David G., Yan, Jiaqiang, Yao, Wang, & Xu, Xiaodong. Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers. United States. doi:10.1038/s41586-019-0957-1.
Seyler, Kyle L., Rivera, Pasqual, Yu, Hongyi, Wilson, Nathan P., Ray, Essance L., Mandrus, David G., Yan, Jiaqiang, Yao, Wang, and Xu, Xiaodong. Mon . "Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers". United States. doi:10.1038/s41586-019-0957-1. https://www.osti.gov/servlets/purl/1513372.
@article{osti_1513372,
title = {Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers},
author = {Seyler, Kyle L. and Rivera, Pasqual and Yu, Hongyi and Wilson, Nathan P. and Ray, Essance L. and Mandrus, David G. and Yan, Jiaqiang and Yao, Wang and Xu, Xiaodong},
abstractNote = {The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect1,2,3, tunable Mott insulators4,5 and unconventional superconductivity6. Moreover, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors7,8,9, but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in a moiré potential in molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers. At low temperatures, we observe photoluminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 microelectronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, –15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at a twist angle of approximately 60 degrees. This is consistent with the umklapp recombination of interlayer excitons near the commensurate 21.8-degree twist angle7. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. Here, we report on opportunities to control two-dimensional moiré optics through variation of the twist angle.},
doi = {10.1038/s41586-019-0957-1},
journal = {Nature (London)},
issn = {0028-0836},
number = 7746,
volume = 567,
place = {United States},
year = {2019},
month = {2}
}

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